* Mel Gorman <[email protected]> wrote:
> On Mon, Jan 25, 2016 at 04:46:35PM +0100, Ingo Molnar wrote:
> > > Of course, it'll be our luck that tracking the data for these
> > > tracepoints is the most expensive part of schedstats ...
> > >
> > > Ingo?
> >
> > IIRC it needed only a small subset of schedstats to make those tracepoints
> > work.
> >
> > We already have too much overhead in the scheduler as-is - and the extra
> > cache
> > footprint does not even show on the typically cache-rich enterprise CPUs
> > most of
> > the scalability testing goes on.
> >
> > My minimum requirement for such runtime enablement would be to make it
> > entirely
> > static-branch patched and triggered at the call sites as well - not hidden
> > inside
> > schedstat functions.
> >
>
> As it is, it's static-branch patched but I'm struggling to see why they
> cannot
> be hidden in the schedstat_* functions which are just preprocessor macros.
> The
> checks could be put in the callsites but it's a lot of updates and I don't
> think
> the end result would be very nice to read.
So I was judging by:
@@ -755,7 +755,12 @@ static void
update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
struct task_struct *p;
- u64 delta = rq_clock(rq_of(cfs_rq)) - se->statistics.wait_start;
+ u64 delta;
+
+ if (static_branch_unlikely(&sched_schedstats))
+ return;
+
which puts a static branch inside a real function, not preprocessor macros.
Thanks,
Ingo
